An image forming apparatus such as a copy machine and a printer based on electrophotography includes a waste toner receiving container that receives waste toner collected from a conveying belt or an intermediate transfer belt. The amount of waste toner that may be received is set in advance in a waste toner receiving container, such that the waste toner receiving toner is replaced with another one when the amount of waste toner reaches a preset amount. The number of operations with respect to the waste toner receiving container may be reduced by detecting the amount of waste toner with high precision, such that various techniques for detecting the amount of waste toner with high precision have been proposed.
In Patent Document 1, an image forming apparatus capable of detecting a full state of waste toner with a simple structure is disclosed. A waste toner receiving container of the image forming apparatus is provided with a light-receiving/emitting unit having a light-emitting element and a light-receiving element, and a reflection plate. If light beams emitted from the light-emitting element are not detected by the light-receiving element after being reflected from the reflection plate, then the image forming apparatus detects that the waste toner is in the full state.
However, in an element referred to as a light-transmission sensor disclosed in Patent Document 1, light beams are blocked by waste toner floating in the waste toner receiving container, resulting in false detection. Thus, full state detection devices that perform detection mechanically rather than optically are proposed in Patent Document 2 and Patent Document 3.
Patent Document 2 discloses a waste toner collecting device capable of detecting a full state of waste toner with high precision. A waste toner collecting container of the waste toner collecting device is provided with a movable member whose position is changed by an increase in waste toner in the waste toner collecting container and a full detector having a sensor to detect a change in the position of the movable member. Patent Document 3 discloses a waste toner collecting container that detects a full state by using a displacement sensor. In an upper portion of the waste toner collecting container is mounted the displacement sensor that detects displacement caused by pressurization of swelling waste toner. Inside the waste toner collecting container, a waste toner conveying means is disposed. If the amount of waste toner reaches a predetermined amount, the waste toner conveying means conveys waste toner horizontally and pressurizes the waste toner to flatten the height.